During a growing period of corn, etc., a triazine-containing herbicide such as atrazine and acetoanilide-containing herbicides such as alachlor and metolachlor have been conventionally used. However, atrazine shows low efficacy to gramineous weeds, and alachlor and metolachlor show low efficacy to broad-leaved weeds. It is therefore difficult at present to control gramineous weeds and broad-leaved weeds together using a single herbicide. Further, the use of these chemicals in combination fails to give any sufficient effect. Moreover, the above herbicides are undesirable in view of an environmental problem due to their high dosage requirement.
On the other hand, it is known that specific benzoylcylohexanedione derivatives have herbicidal activity (see JP-B-1-30818, JP-A-61-155347, JP-A-1-143851, JP-A-3-120202, EP 135,191, EP 186,118A, EP 186,119A, U.S. Pat. No. 4,954,165, GB 2,215,333A, EP 336,898A, U.S. Pat. Nos. 4,937,386, 4,780,127, 5,092,919 and PCT International Publication 90/05712). Typical examples of the above benzoylcyclo-hexanedione derivatives are as follows. ##STR2##
Further, JP-A-64-6256 discloses cyclohexanedione derivatives having a fused dicyclic group containing heteroatoms. ##STR3##
However, cyclohexanedione derivatives having a thiochroman ring such as compounds of the present invention are not known yet.
Further, the cyclohexanedione derivatives that have been already disclosed are insufficient in practical use, particularly poor in herbicidal activity to gramineous weeds such as barnyardgrass and green foxtail.
It is therefore a first object of the present invention to provide a novel cyclohexanedione derivative which exhibits high selectivity for corn, wheat and barley and can control both gramineous weeds and broad-leaved weeds at low dosage.
It is a second object of the present invention to provide a process for the production of the above novel cyclohexanedione derivative.
Further, it is a third object of the present invention to provide a herbicide containing the above novel cyclohexanedione derivative as an active ingredient.